Conventionally, resins excellent in transparency and mechanical characteristics have been used widely as optical materials for engineering plastics. For example, poly(methyl methacrylate) (hereinafter referred to as PMMA), polycarbonate (hereinafter referred to as PC), and amorphous polyolefin (hereinafter referred to as AOP) are used as optical materials for compact discs, laser discs, projection lenses, f-θ lenses, photographic system lenses, finder lenses, pick-up lenses, digital camera lenses, micro lens arrays, etc., and also as transparent parts and reflection materials of automobiles. PMMA has the advantage of good transparency and small optical anisotropy and is therefore used popularly, however is disadvantageous in that it is highly hydroscopic and is often deformed and inferior in the shape stability after molding.
On the other hand, PC has the advantage of high heat resistance and good transparency, however is disadvantageous in that its fluidity is low and the birefringence of its moldings is often large and accordingly, it cannot be said that PC is sufficiently satisfactory for use as optical materials. APO has the advantage of good heat resistance and transparency, however is disadvantageous in that its fluidity is low and it is colored easily at the time of molding. Further, in the case of sticking a vapor deposition film or a hard coating film, unless being subjected to pretreatment such as plasma treatment, APO cannot be provided with sufficient adhesion strength and therefore, it cannot be said that APO is sufficiently satisfactory for use as optical materials.
Further, in recent years, optical disks and digital video disks for recording and regenerating information of sound, images, letters and the like using laser beam have been developed and substrate materials having further higher optical characteristics have been desired. Miniaturization of photographic system lenses of digital cameras and compact cameras to be used for mobile phones has been advanced and also miniaturization and high precision and fineness of image recognition apparatus such as CCD and CMOS have been tried advantageously, resin materials with lower optical anisotropy have been desired.
As polyester polymers and polyester copolymers for the optical materials, polymers of aromatic dicarboxylic acids and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorenes are proposed (e.g. Japanese Patent No.2843215 and No.2843214). Also, polymers of alicyclic dicarboxylic acids and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorenes are proposed (e.g. Japanese Patent No.3331121 and Japanese Publicated Application H11-60706 and 2000-319366). Since these polyester copolymers have high refractive index, small birefringence and excellent heat resistance and transparency, they are useful for optical materials, but in the case of industrial production, the physical properties such as the heat resistance are sometimes fluctuated in a wide dispersion and therefore, there is a problem that the quality could not be stabilized.
As a production method of an alicyclic dicarboxylic acid to be used as a raw material, is known a method involving forming an alkali metal salt of a high purity terephthalic acid in the case, for example, of 1,4-cyclohexanedicarboxylic acid, hydrogenating the salt, and neutralizing the obtained product with an acid. As the acid to be employed for the neutralization, sulfuric acid and hydrochloric acid (e.g. Japanese Publicated Application H07-507041) are exemplified. As a production method of 1,4-cyclohexanedicarboxylic acid without using sulfuric acid or hydrochloric acid, a method involving carrying out hydrogenation in the presence of a catalyst and removing impurities by bringing the produced compound into contact with steam (e.g. Japanese Publicated Application H06-184041) is known.
As a production method of, for example, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene as a dihydroxy compound to be used as a raw material for polyester polymers is reported a method of synthesizing it from fluorene with bisphenoxyethanol using thioacetic acid, β-mercaptopropionic acid, or sulfuric acid as an assisting catalyst or a catalyst (e.g. Japanese Publicated Application H07-165657 and H10-17517).
However, in the case of conventional polyester polymers, depending on the situation, problems of extreme slowing down of the reaction speed during the production; deterioration of heat resistance; and coloration of resin, e.g. yellowing, are sometimes observed.